Mazda 3 engine bay rattle / knocking noise appearing only between 1500-2000 rpm

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Mazda 3
Hello everyone, I'm sorry in advance if this kind of thread has been posted before, I couldn't find it.
So any way I have a Mazda 3 2010 1.6tdi about two months ago it started making this really annoying noise at 1500-2000rpm. Sometimes it's louder sometimes it's quieter and on the rainy days or when drive over a very deep puddle it disappear all together for days. It had a cambelt changed since this problem appeared with a new tensioner and all that. I have two videos which might indicate what the problem can be but me myself I can't figure it out. Do you have a clue what it might be please?

https://www.youtube.com/watch?v=5MjFA82Ztoo

https://www.youtube.com/watch?v=Ho53GqLh0s4
 
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2014 Mazda3 S GT auto, 2008 MX5 6-speed
Can you hear it when revving the engine in neutral or Park? Are the motor mounts okay?
 
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Mazda 3
Can you hear it when revving the engine in neutral or Park? Are the motor mounts okay?
Thank you for you reply! Yes the mounts are perfectly fine. And there is no noise whilest raving in neutral. I've check for error codes yesterday and had a whole lot of things failing amongst which were Maf and O2 sensor. Took an air filter off today to find that the Maf sensor, the hose and the air filter were covered lightly in oil. So I'm guessing that is where the problem lies.
 
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1963 Mercedes 190Dc
If you plan on cleaning the MAF sensor make sure you get MAF specific cleaner, other cleaners (like brake clean) can destroy a MAF sensor.
 
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Mazda 3
Thanks for you reply!
Cleaned my Maf sensor yesterday now it's all lovely and clean few errors disappeared of the system. However the noise is still present. Next on the list will be EGR cleaning, oil change along with the oil filter and finally might have to take a look at the Intake Manifold flaps as sometimes they might come loose and create that flapping sound during hard acceleration and engine load. To be continued...
 
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Mazda 3
So two days ago in a moment of desperation I took the whole air intake system apart only to find out that majority of sensors and air ways were badly covered in a mixture of oil and carbon build up. I bought this car second hand and it just tells me that previous owner had never changed oil in it. So using the Wynns Injector Cleaner Diesel I sprayed all air intake hoses and sensors cleaned hoses with the rag and reinstalled it all back. Also a Redex Oil Stop Leak was added to the engine oil to stop a very tiny leak that I had from a gasket. Took my car for a near 200 mile ride yesterday and I'm pleased to announce that the annoying rattling sound is nearly gone and for now became by far less noticeable then before. So the cleaning of sensors and air intake did a good job. I'm planing further maintenance this month with the oil and a filter change which should complete the job nicely.
 
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2014 Mazda3 S GT auto, 2008 MX5 6-speed
I wonder why air intake passageways would have oil in them. Could it be that the previous owner had a K&N air filter installed that was over-oiled? This could adversely affect the MAF. Not changing the engine oil should not do this, although it could result in excessive engine wear. Now the throttlebody and/or intake manifold could contain engine oil if excessive blowby in the crankcase cannot be adequately prevented from getting past the PCV valve. Excessive blowby past the piston rings could be the result of not changing the oil.
 
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Mazda 3
I wonder why air intake passageways would have oil in them. Could it be that the previous owner had a K&N air filter installed that was over-oiled? This could adversely affect the MAF. Not changing the engine oil should not do this, although it could result in excessive engine wear. Now the throttlebody and/or intake manifold could contain engine oil if excessive blowby in the crankcase cannot be adequately prevented from getting past the PCV valve. Excessive blowby past the piston rings could be the result of not changing the oil.
I will be flushing the engine, changing oil, air and oil filter and will have all of the air ways cleaned out completely next weekend. We'll see what happens next. Also noticed that sound disappeared completely after filling the fuel tank to the top.
 
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Mazda 3
I will be flushing the engine, changing oil, air and oil filter and will have all of the air ways cleaned out completely next weekend. We'll see what happens next. Also noticed that sound disappeared completely after filling the fuel tank to the top.
So a quick update on the situation. Flushed the engine followed by fresh Castrol Edge Titanium oil, MAN oil filter and fresh MAN air filter and Oil aditive. As well as cleaned all the sensors and airways including turbo blades. The engine performance increased dramatically car goes up the hill like a dream and gets up to desired speed in no time. The slight noise is still there I'll give it couple of days to a week and then will come back for a further report on the situation. But at the minute revs are stable and I can tell that engine breathes much better.
 
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